We hear a lot about the advancements in aerospace computing technology since the Saturn V flew for the Apollo missions. What is less talked about, is the revolution in welding. When the Saturn V was being constructed, the typical gas arc welding that is common in today’s manufacturing, was cutting edge at the time.
However, NASA had a problem...
Gas arc welding usually leaves small pores in the finished product. These small pores are fine in the chassis of a car, but are catastrophic for the body of the crew capsule hurling over 15,000 mph away from Earth. It was an incredible feat of engineering that the weld problem was able to be solved with the manufacturing processes of the time.
Through incredible precision, skill, and testing NASA was able to create a safe welding process. However, this process was still very limited in its ability to combined dissimilar materials of different thicknesses. This resulted in having to default to the larger of the two materials and plenty of unnecessary weight in the 6 million pound rocket.
For years the cost of getting humans or material to space was astronomically expensive, excuse the pun. One of the main bottlenecks of lowering the cost was this welding issue.
Then along came SpaceX
Introducing Friction Stir Welding
Friction stir welding is a solid-state joining process that joins together surfaces with no heat, sparks or flames. The process relies on high pressure and agitation of the surfaces to be joined. It may also use ultrasonic vibrations and pumps for agitation, though usually these are not necessary in most cases.
SpaceX was founded to be the low cost, commodity alternative to expensive aerospace companies. They saw the cost saving potential of fiction stir welding and incorporated it into their early Falcon 9 rocket.
Advantages of friction stir welding are:
- No heat input required
- Can be used for dissimilar materials, as long as they can fit into the tool
- Generally good quality welds are produced with limited need for post processing
- Good fatigue strength of joints
- High shear strength between metals that have low
The result: a great process for aerospace
This makes friction stir welding great for aerospace. The high quality joints adhere to the rigorous safety needed for space flight. Furthermore, the ability to weld with dissimilar materials allows for super light aluminum alloys to fly in situations where more expensive metals would have historically been required. Friction stir welding increases the speed of high quality manufacturing, which is necessary for companies constantly rebuilding rockets for launch.
This type of welding also uses no heat input which makes it safe to use for the expensive alloys used by aerospace contractors. Currently, there are a wide variety of materials that can be used with friction stir welding such as titanium, aluminum, steel, and more.
SpaceX certainly didn’t invent FSW, but their strategy for low cost space travel was the perfect application of the manufacturing. The process was developed by Sandia National Laboratories in 1980s and has been reviewed and discussed by the Friction Stir Processing Committee of Materials Science and Engineering (MSE) Division, ASME. The first commercial use came from Lockheed Martin's Missile and Space Operations Co., Sunnyvale, Calif., in 1992, using a portable system to make thin-walled aluminum rocket motor cases. The first full-production friction stir w elding system was introduced by FSW Corporation (formerly SPEAG), of Jona Switzerland, at the "Friction Stir 2000" conference in November 2001, following more than 15 years of development work. SpaceX wouldn’t launch a true friction stir welded product until their Falcon 9 launched in 2010.
There are reasons that friction stir welding hasn’t become main stream in other manufacturing processes.
Disadvantages to friction stir welding are:
- Slower than traditional welding technique
- Limited to certain material thicknesses
- Low penetration depths, especially with thicker materials
- High tooling costs
- Difficulties joining thick-walled parts without buckling due to large shear forces acting perpendicular to the weld interface
The speed, limitations, and cost mean that friction stir welding will likely stay a niche manufacturing process for the foreseeable future.